selectVariant

Select the representation variant that best matches the request. More
explicit variants are chosen ahead of less explicit ones. A vary header
is computed from the supplied list and automatically added to the
response.

null if the preconditions are met or a ResponseBuilder set with
the appropriate status if the preconditions are not met. A returned
ResponseBuilder will include an ETag header set with the value of eTag.

lastModified - a date that specifies the modification date of the resource

eTag - an ETag for the current state of the resource

Returns:

null if the preconditions are met or a ResponseBuilder set with
the appropriate status if the preconditions are not met. A returned
ResponseBuilder will include an ETag header set with the value of eTag.